The present invention relates to a catalytic partial oxidation process for producing synthesis gas (mixtures containing H2 and CO) via Catalytic Partial Oxidation (CPO) starting from liquid and gaseous fuels and an oxidizing stream, containing oxygen (for example, pure oxygen, air or enriched air).
The main technologies for the production of synthesis gas (prevalently consisting of a mixture of H2 and CO with smaller quantities of H2O, CO2 and CH4) can be classified as the following technologies:                a) non-catalytic partial oxidation (PO) of heavy hydro-carbons (Falsetti, J. S., Hydrocarbon Technology International, 1993, page 57)        b) steam and CO2 reforming (SR) (Rostrup-Nielsen, J. R. “Catalytic Steam Reforming”, in Catalysis Science and Technology, J. R. Anderson, M. Boudart Eds. Vol. 5, Springer, Berlin 1988, page 1)        c) autothermal reforming (ATR) (T. S. Christensen I. I. Primdahl, Hydrocarbon Processing, March 1994, page 39).        
Steam reforming (SR) is used for converting natural gas (NG) and naphthas into synthesis gas mainly according to reactions [1-2]. Before being sent to SR, the hydrocarbon reagent is preheated and desulfurated; vapour is then added and the mixture is further preheated. The reforming takes place in an oven in which there are tubes filled with catalyst, through which the reaction mixture flows. The synthesis gas at the outlet of the tubes is rapidly cooled and can be sent to water-gas shift processes [3] and separation/purification.CH4+H2O=CO+3H2 ΔH298=206.36 kJ(mole)  [1]CnHm+nH2O=nCO+(m/2+n)H2  [2]CO+H2O=CO2+H2 ΔH298=−41.16 kJ(mole)  [3]
The main uses of SR are:                in the production of H2 for refinery uses;        in the synthesis of ammonia;        in the synthesis of methanol.        
Autothermal reforming (ATR) combines sub-stoichiometric combustion reactions of NG [4] which take place in a combustion chamber, with SR and CO2 reforming reactions [5] which take place in a catalytic bed situated after the combustion chamber.CH4+3/2O2=CO+2H2O  [4]CO2+CH4=2CO+2H2  [5]
ATR is used for producing synthesis gas from NG for methanol synthesis, Fischer-Tropsch and carbonylation processes. The ATR technology requires the use of pure oxygen or strongly enriched air for preventing the decrease in the partial oxygen pressure in the combustion chamber from causing the formation of carbonaceous residues. Furthermore, as the lighter the hydrocarbon charge, the easier the formation of carbonaceous residues, ATR can treat only NG directly, with considerable limitations on the vapour/carbon and oxygen/carbon conditions in the feeding. If the content of C2+ in the NG is significant, a performing passage is necessary to eliminate them.
PO technologies, on the other hand, are capable of converting into synthesis gas, a wide range of hydrocarbon charges, from NG to gas oils, from heavy residues to coal. The process can be represented with the reactions [6-7].CH4+½O2=CO+2 H2ΔH298=−35.69 kJ/mole  [6]CnHm+n/2O2=nCO+m/2H2  [7]
When the use of partial oxidation is extended to the oxidation of heavy residues and coal, these are gasification processes which can be represented by the equations [8, 9]C+½O2=CO ΔH298=−110.62 kJ/mole  [8]C+H2O=CO+H2 ΔH298=131.38 kJ/mole  [9]
The PO technology, however, has a higher energy consumption than that of SR and STR catalytic technologies and also requires the use of complex and costly equipment. The absence of a catalyst in the area below the combustion chamber causes, in fact, much higher temperatures at the outlet of the reactors (around 1400° C.) from which it is difficult to effectively recuperate the heat. The most advantageous PO applications are therefore those which transform hydrocarbon charges consisting of heavy hydrocarbon residues from oil processing which cannot be transformed into synthesis gas by means of the SR and STR catalytic technologies. The PO technology can use air, enriched air or oxygen as oxidizing agent but it is preferable to use pure oxygen to limit the formation of carbonaceous residues which, although tolerated, are formed in a percentage which increases with the increase in the N2 content in the reagent mixture and the lower the vapour/carbon and H/C ratios in the hydrocarbon charge. The carbonaceous residues, however, are eliminated with washing operations of the synthesis gas. Due to the high temperatures in the combustion chamber, the presence of N2 subsequently causes the formation of NOx.
A technology which is still not widely used but which is frequently the object of R&D projects is catalytic partial oxidation (CPO) with a short contact time. This allows the production of synthesis gas from air and from a large number of hydrocarbon reagents without the formation of undesired by-products such as carbonaceous residues and NOx.
CPO with a low contact time is based on the reactionCH4+½O2=CO+2 H2ΔH°=−36 kJ/mole  [10]slightly exothermic. The reaction was studied for converting NG into synthesis gas also using low vapour/carbon, oxygen/carbon ratios and using air, enriched air or oxygen as oxidizing agent. This process allows most of the reactions leading to the formation of carbonaceous residues to be avoided. As the reactions take place at temperatures lower than 1400° C., NOx is not formed even if air is used as oxidizing agent.
The process for the production of synthesis gas with a short contact time is described in various documents of scientific and patent literature: (a) M. Bizzi, L. Basini, G. Saracco, V. Specchia, Ind. Eng. Chem. Res. (2003), 42, 62-71 “Modelling a transport phenomena limited reactivity in short contact time catalytic partial oxidation”; (b) L. Basini, K. Aasberg-Petersen, A. Guarinoni, M. Oestberg, Catalysis Today (2001) 64, 9-20 “Catalytic Partial Oxidation of Natural Gas at Elevated Pressure and Low Residence Time”; (c) H. Hickman, L. D. Schmidt, J. Catal. 138 (1992) 267; (d) D. Hichman, L. D. Schmidt Science, 259 (1993) 343; (e) L. Basini, G. Donati WO 97/37929; (f) Sanfilippo, Domenico; Basini, Luca; Marchionna, Mario; EP-640559; (g) D. Schaddenhorst, R. J. Shoonebeek; WO 00/00426; (h) K. L. Hohn, L. D. Schmidt, S. Reyes, J. S. Freeley, WO 01/32556; (i) A. M. Gaffney, R. Songer, R. Ostwald, D. Corbin, WO 01/36323.